The development of magnetic bubble devices has reached the stage of commercial use, particularly for the storage of sequentially retrievable data in communications and data processing equipment.
Magnetic bubble devices typically comprise a flat, nonmagnetic substrate of a material such as, e.g., gadolinium-gallium garnet, nominally Gd.sub.3 Ga.sub.5 O.sub.12, and a layer of a magnetic garnet material which is epitaxially deposited on the substrate and whose easy direction of magnetization is perpendicular to the layer. In the presence of a suitable magnetic bias field parallel to such direction, the layer is capable of sustaining small domains, called bubbles, which are magnetized in a direction opposite to the direction of the bias field. Desirable domains typically have right circular cylindrical shape and extend from near the surface of the magnetic film to the vicinity of the film-substrate interface. Bubble diameter may be approximately equal to the thickness of the film.
Device operation typically involves the nucleation, propagation, and detection of magnetic bubbles, propagation being along paths or tracks which may be defined, e.g., by magnetic overlays, by a pattern of locally modified magnetic properties in the layer, or by a conductor overlay as disclosed in the paper by A. H. Bobeck et al., "Current-Access Magnetic Bubble Circuits", Bell System Technical Journal, Vol. 58, No. 6, July-August 1979, pp. 1453-1540.
Preferred for the deposition of magnetic garnet layers on a substrate is a method of liquid phase epitaxy, involving controlled growth from garnet constituents in flux solution as disclosed in U.S. Pat. No. 3,790,405, issued Feb. 5, 1974 to H. J. Levinstein. Properties of resulting layers such as, e.g., thickness, defect density, magnetization. coercivity, anisotropy field, and bubble diameter, stability, and mobility are dependent on growth conditions such as, e.g., melt composition, growth temperature, and growth procedure as discussed in papers by S. L. Blank et al., "Kinetics of LPE Growth and its Influence on Magnetic Properties", AIP Conference Proceedings, Vol. 10 (1974), pp. 255-270; S. L. Blank et al., "Preparation and Properties of Magnetic Garnet Films Containing Divalent and Tetravalent Ions", Journal of the Electrochemical Society, Vol. 123, No. 6, June 1976, pp. 856-863; and S. L. Blank et al., "The effect of Melt Composition on the Curie Temperature and Flux Spin-Off from Lutetium Containing LPE Garnet Films", IEEE Transactions on Magnetics, Vol. MAG-13, No. 5, September 1977, pp. 1095-1097.
As disclosed in papers cited above, a PBO--B.sub.2 O.sub.3 flux has been preferred for garnet growth, such preference being due, at least in part, to nonwetting of a growing garnet layer by the flux. As disclosed in U.S. Pat. No. 4,165,410, issued Aug. 21, 1979 to S. L. Blank, wetting fluxes such as, e.g., a boron oxide-bismuth oxide flux are not precluded.
As magnetic device technology progresses towards increasingly higher bit densities, layer specifications change; in particular, specified layer thickness decreases as shown, e.g., in the paper by S. L. Blank et al., "Design and Development of Single Layer, Ion-Implantable Small Bubble Materials for Magnetic Bubble Devices", Journal of Applied Physics 50, March 1979, pp. 2155-2160.
Relevant with respect to the invention is a phase diagram of the PbO--V.sub.2 O.sub.5 system as shown by E. M. Levin et al., "Phase Diagrams for Ceramists", American Ceramic Society, p. 117.